1. Field of the Invention
The present invention relates to a method and a unit for computing a charging efficiency of a battery used for supplying an electrical power to a load at any point between a start and an end of charging of the battery. The charging efficiency is defined as a ratio of an electrical quantity charged in the battery to a total electrical quantity supplied to the battery. The invention also relates to a method and a unit for knowing an electrical quantity charged in the battery based on a plurality of the obtained charging efficiencies.
2. Related Art
For example, in a battery mounted on a motor car, particularly in an electric car having an electric motor as a primary driving unit, it is greatly important to monitor a state of charge (SOC) of the battery to ensure a normal operation condition of the car.
Recently, in a general car having an engine as a driving unit or in a hybrid car having an electric motor for providing an additional driving force to an engine, it has been developed to have an idling function during an engine stop condition, e.g. when the car must temporally stop at an intersection of roads according to a stop signal.
A car having such an idling function requires a battery which can have a discharging capacity enough for restating its engine after the battery has discharged a considerable amount of electrical power for driving a power assisting motor (cell motor) during an idling operation of the car.
Therefore, it is greatly important to correctly know a state and a remaining discharging capacity of a battery concerning a general car and a hybrid car as well as the electric motor car described above.
In a typical electric car, a battery is charged during a non-usage state of the car, e.g. in a garage. In the meantime, a hybrid car has a motor generator which functions a generator to charge a battery when the car is running by a primary engine. The motor generator can also charge the battery at a deceleration period of the car even when the car is running by the driving force of the motor generator. A general car having only a primary engine charges its battery by an alternator driven by the engine.
Accordingly, regardless of the car type such as an electric car, a general car, or a hybrid car, it is important to correctly know a charged state of its battery, because the charged state varies with a charging operation as well as an electrical power supply to a load.
However, a chemical reaction during charging of a battery generates an oxygen gas and a hydrogen gas which are reduced into H2O, so that an electrical quantity supplied into the battery is not partially used for charging the battery. Furthermore, this tendency is more apparent when the battery gets nearer to its full charged state. Thus, a mere integration of charging currents with corresponding times can not obtain a correct charged state of the battery at a point during the charging of the battery.
The above-mentioned problem is not limited in an on-vehicle battery but also appears in a general battery supplying an electrical power to a load.
In view of the above-mentioned situation, an object of the invention is to provide a method and a unit for obtaining a charging efficiency of a battery used for supplying an electrical power to a load at any point between a start and an end of charging of the battery. The charging efficiency is defined as a ratio of an electrical quantity charged in the battery to a total electrical quantity supplied to the battery. The invention also provides a method and a unit for correctly computing an electrical quantity charged in the battery. This can correctly know a charged state of the battery at any point of charging of the battery.
For achieving the object, a first aspect of the invention is a method for computing a charging efficiency, which is a ratio of an electrical quantity charged in a battery as an electromotive force to a total electrical quantity supplied to the battery, at any one point in time between a start and an end of charging of the battery, the method comprising:
measuring an initial resistance of the battery at the start of the charging,
measuring a voltage and a current between a pair of terminals of the battery at the one point to obtain an inner resistance of the battery at the one point,
obtaining a resistance difference which is a difference of the inner resistance at the one point and the initial resistance, and
obtaining a ratio of the resistance difference to a full charged state resistance that is a resistance of the battery at a full charged state of the battery,
whereby, a charging efficiency of the battery at the one point is computed based on the ratio.
Thus, a voltage and a current are measured between the pair of terminals of the battery at a plurality of measuring points between a start and an end of charging of the battery, to obtain an resistance of the battery at each of the measuring points. Then, a resistance difference, which is a difference of a resistance at the charge start point and a resistance at one of the measuring points, is obtained. Furthermore, a full charged state resistance at a full charged state of the battery is obtained, and a ratio of the resistance difference to the full charged state resistance is obtained to know a charging efficiency of the battery at each of the measuring points during charging of the battery. This can correctly know a charged state of the battery, which would be varied with a gas generated in the battery. That is, the charging efficiency includes a charging loss due to the gas generation varying with a charging stage.
In a second aspect of the invention according to the first aspect, the ratio of the resistance difference to the full charged state resistance is deducted from 1 (one) to provide a charging efficiency at the one point.
Thus, a drop of the charging efficiency from an ideal value can be computed at any point during the charging by using the terminal voltage and the discharging current which are measured during the charging.
A third aspect of the invention is a method for computing a charged electrical quantity of the battery according to the first aspect of the invention, wherein a charged electrical quantity stored in the battery at the charging end of the battery is obtained by using a plurality of the charging efficiencies each obtained at each of a plurality of the measuring points in time between the start and the end of charging of the battery.
In the third aspect of the invention, a charged electrical quantity at any point during charge of the battery is obtained based on the charging efficiencies sequentially obtained over the start and the end of charging of the battery according to the first aspect of the invention.
Thus, an electrical quantity actually charged in the battery as compared with an electrical quantity supplied to the battery is correctly computed at each selected point during a time interval. An integration of the charged electrical quantities from the start to the end of the charging correctly provides a final electrical quantity charged in the battery.
A fourth aspect of the invention is a method for computing a charged electrical quantity according to the first aspect of the invention, wherein the battery has poles that are in an active state where no passivating film is formed on the poles, and whether the poles are in the active state is determined based on a pattern of the charging current varying with time during the charging,
the charged electrical quantity charged in the battery being obtained by using a plurality of the charging efficiencies each obtained at each of a plurality of the measuring points in time between the start and the end of charging of the battery when the poles are in the active state,
the charged electrical quantity of the battery being obtained based on an integration of a charging current multiplied by a corresponding charging time during a transition period in which a passivating film remains on the poles of the battery before the charging current sufficiently breaks the passivating film.
The battery is not in an active state when a passivating film is formed on poles of the battery at the start of charging of the battery. In the inactive state, a charging current becomes smaller so that no gas is generated in the battery. With the charging operation, the passivating film breaks so that the charging current increases.
Thus, the charged electrical quantity of the battery is obtained based on an integration of the charging current multiplied by a corresponding charging time during a transition period in which the battery is in an inactive state. In the meantime, the charged electrical quantity of the battery is obtained based on the charging efficiencies sequentially obtained over the start and the end of charging of the battery when the battery is in the active state where no passivating film remains on the poles of the battery.
Referring to FIG. 1, a fifth aspect of the invention will be discussed. The invention is a unit for computing a charging efficiency, which is a ratio of an electrical quantity charged in a battery 13 as an electromotive force to a total electrical quantity supplied to the battery, at any one point in time between a start and an end of charging of the battery, the unit comprising:
a measuring device A for measuring a voltage and a current between a pair of terminals of the battery at the one point to obtain an inner resistance of the battery at the one point,
an initial resistance computing device 23A for obtaining an inner resistance of the battery at the charging start based on a terminal voltage and the corresponding current which are measured by the measuring device,
an on-charging resistance computing device 23B for obtaining an inner resistance of the battery at the one point based on a terminal voltage and a corresponding current which are measured by the measuring device,
a resistance difference computing device 23c for obtaining a difference between of the inner resistance at the one point and the initial resistance,
a storage device 23cA for storing an inner resistance at a full charged state of the battery, and
a resistance ratio computing device 23D for obtaining a ratio of the resistance difference to the full charged state resistance,
whereby, a charging efficiency of the battery at the one point is computed based on the ratio.
In the fifth aspect of the invention, the measuring device A measures a voltage and a corresponding current between a pair of terminals of a battery 13 at a plurality of measuring points between a start and an end of charging of the battery. The resistance computing device 23A or 23B obtains a resistance of the battery at each of the measuring points based on the voltages and the corresponding currents between the pair of terminals of the battery. The resistance difference computing device 23C obtains a resistance difference which is a difference of a resistance at the charge start point and a resistance at one of the measuring points. The storing device 23cA stores a reference full charged state resistance at a full charged state of the battery, and the resistance ratio computing device 23D obtains a ratio of the resistance difference to the reference full charged state resistance. This can correctly know a charged state of the battery 13, which would be varied with a gas generated in the battery.
Thus, a battery charging efficiency at any point during the charging is correctly computed by using the terminal voltage and the discharging current which are measured during the charging. The charging efficiency includes a charging loss due to the gas generation varying with a charging stage.
A sixth aspect of the invention is a unit for computing a charging efficiency according to the fifth aspect of the invention wherein the resistance ratio computing device deducts the ratio of the resistance difference to the full charged state resistance from 1 (one) to provide a charging efficiency of the battery at the one point.
Thus, a drop of the charging efficiency from an ideal value can be computed at any point during the charging by using of the terminal voltage and the discharging current which are measured during the charging.
A seventh aspect of the invention is a unit for computing a charged electrical quantity according to the fifth aspect of the invention, wherein a charged electrical quantity stored in the battery at the charging end of the battery is obtained by using a plurality of charging efficiencies each obtained at each of a plurality of sequential points in time between the start and the end of charging of the battery by means of the charging efficiency computing unit.
In the seventh aspect of the invention, a charged electrical quantity at any point during charge of the battery 13 is obtained based on the charging efficiencies sequentially obtained over the start and the end of charging of the battery 13. Thus, an integration of a charged electrical quantity from the start to any point of the charging provides a charged electrical quantity at the charging point, obtaining a correct electrical quantity actually charged in the battery by an electrical power supplied into the battery 13.
Thus, an integration of the charged electrical quantity from the start to the end of the charging provides a final electrical quantity charged in the battery.
An eighth aspect of the invention is a unit for computing a charged electrical quantity according to the fifth aspect of the invention, wherein the battery has poles that are in an active state where no passivating film is formed on the poles, and the charged electrical quantity computing unit further comprises:
an active state determining device 23E for determining whether the poles are in the active state based on a pattern of the charging current varying with time during the charging, the charging current obtained by the measuring device, the charged electrical quantity charged in the battery being obtained by using a plurality of charging efficiencies each obtained at each of a plurality of sequential points in time between the start and the end of charging of the battery when the poles are in the active state, and
a charged electrical quantity computing device 23F for obtaining a charged electrical quantity during a transition period in which a passivating film remains on the poles of the battery so that the poles are not in the active state before the charging current sufficiently breaks the passivating film, the charged electrical quantity of the battery being obtained based on an integration of a charging current multiplied by a corresponding charging time during the transition period.
The battery 13 is not in an active state when a passivating film is formed on poles of the battery at the start of charging of the battery. In the inactive state, a charging current becomes smaller so that no decrease of the charging efficiency of the battery due to a gas generated in the battery occurs. With the charging operation, the passivating film breaks so that the charging current increases. The active state determining device 23E determines whether the battery is in the active state based on a pattern of the charging current varying with time.
Thus, the charged electrical quantity of the battery 13 is obtained based on an integration of the charging current with a corresponding charging time during a transition period in which the battery 13 is in an inactive state. Therefore, an electrical quantity charged in the battery is correctly computed during a transition period until the passivating film is completely broken by the supplied current. In the meantime, the charged electrical quantity of the battery 13 is obtained based on the charging efficiencies sequentially obtained over the start and the end of charging of the battery 13 when the battery 13 is in the active state where no passivating film remains on the poles of the battery 13.